Physics Flashcards
1mCi=
37 MBq
Auger effect
When electron drops a level to fill a sudden vacancy energy is not emitted but transmitted to another electron ejecting it too - AUGER ELECTRON
Characteristic X-rays
Occur when an inner shell electron is ejected and its vacancy is filled by another electron
Curie (Ci)
Radioactivity - disintegrations per second 1mCi=37MBq
Roentgen
Radioactivity exposure - radiation in environment
Gray (Gy)
Radiation dose
1 Gy=100 RAD
(Radiation Absorbed Dose)
REM
Radiation absorbed by tissue
(Radiation Equvalent Man)
100 RAD=100 REM=1 Sv
Z
Atomic number (# protons)
A
Atomic mass
201Tl energy emssion
80 keV mercury X-rays
99mTc energy emission
140 keV gamma
17 segment model
Recombination zone
in gas-filled detector
unusable – higher probability of recombination of ion pairs than their detection
Geiger-Mueller counter
* output independent of absorbed energy
* used for survey meters
* 10x more sensitive than ion chamber
NaI scintillator
- dense – good absorber of gamma-rays
- efficient scintillator – 30 photons/keV
- light output proportional to amount radiation absorbed
- very fragile
Gamma camera energy resolution at 140 keV
9-11%
FWHM
Full width at half maximum – curve spread at the location 50% down on each side from peak amplitude
Collimator
Septa between holes absorb photons travelling in oblique lines so they never strike the detector
Gamma-camera ENERGY correction
- Decreases the system’s FWHM
- improves contrast (ability to resolve 2 points in space)
Gamma-camera LINEARITY correction
- PMT has a non-linear response to light across its face
- increased sensitivity at edges compared to center
- consequently, events at edges are misposition toward the center of the PMT
Gamma-camera UNIFORMITY correction
- aquire a high-count flood
- measure the average counts per pixel
- for each pixel compute a correction factor
- store corrections as a uniformity correction map
- correct clinical studies by multiplying each pixel in the image by its corresponding factor from the map
Parallel-hole collimator response to radiation
Collimator specs
1) energy (keV);
* thinkness of septa and materials used*
2) spacial resolution
* FWHM of 1 mm pint source @ 10 cm away*
3) sensitivity
* CPS/mCi (counts/second/radiation)*
Parallel-hole collimator design
System resolution
Rs2=Rc2 + Ri2
Rc (collimator) ~ 8 mm
Ri (instrinsic) ~ 3 mm
Rs (system) ~ 8.5 mm
Effect of source to collimator distance
Degrades resolution but not sensitivity
Non-standard collimators
New design collimators
Angular sampling
How many projections
(recommended # is 64)
Star artifact
Filtered backprojection
Mathematical filter to remove star artifact
(RAMP FILTER)
Point response function
RAMP artifact
FREQUENCY DISTRIBUTION
in SPECT imaging
low frequency = gross objects
mid frequency = detail + noise
high frequency = noise + detail
Effect of UNDERFILTERING
- can create lesions
- cut-off frequency set too high
Effect of OVERFILTERING
- can mask a lesion
- cut-off frequency set too low
ISOBARS
isobar – equal “a” nucleons
9943Tc and 9942Mo
ISOTOPES
Isotopes - Equal Protons (z)
ISOTONES
Isotones - Equal neutrons (a - z)
ISOMERS
Isomers – same radionuclide, but different energy state
99mTc (metastable) and 99Tc
BETA- emission
BETA+ emission
ELECTRON CAPTURE
admissible 99Mo breakthrough
<0.15 uCi/1 mCi Tc (at time of dose administration)
Aluminum +++
admissible impurity level
<10 PPM
admissible HRTC (hydrolyzed reduced Technetium)
<2%
Effective t1/2 formula
1/effective half-life = 1/biologic half-life + 1/radioactive or physical half-life.
Physical t1/2 formula
Physical t ½ = 0.693/x (decay constant)
Technetium production/decay
Production: Reactor → Generator (parent 99Mo)
Decays: Gamma decay
Thallium production/decay
Production: Cylcotron (parent 201Pb)
Decays: Electron capture (decays to 201Hg)
18-FDG production/decay
Production: Cyclotron
Decays: Beta + decay (Positron)
STOCHASTIC
Stochastic (probabilistic)
The probability, not severity, of occurrence increases with dose
- Severity is not related to magnitude of dose
- No threshold dose
- Any dose is assumed to carry some risk
DETERMINISTIC
Non-stochastic (deterministic)
Severity of ailment increases with dose
- Known threshold dose of disease induction
- Severity increases above that threshold
- Examples: Skin injury, cataract formation
background radiation exposure values
~360 mRem/year (1 mRem/day)
~300 from natural
~60 from artificial sources
maxiumum allowed radiation exposure
RADIATION WORKERS: 5 Rem/year
Meds that inhibit binding of the Tc-99 pertechnetate to the hemoglobin
- hydralazine
- prazosin
- heparin
- digoxin
LVEF by ERNA
*equilibrium radionuclide angiocardiography *
LVEF = Background corrected end diastolic counts – Background corrected end systolic counts/ Background corrected end diastolic counts
LEHR Collimator efficiency
1:10,000 (0.01% )
How often to check
frequency of energy peaking for a gamma camera?
daily
PMT structure
Image reconstruction process flow
Thirty-two to sixty-four planar projections are acquired 180 degrees around the patient perpendicular to the long axis of the body, and the initial reconstruction is into the transaxial plane. From these transaxial images, the long axis of the heart is defined, and subsequently the conventional vertical and horizontal long-axis and the short-axis images are reconstructed for analysis.
SPECT image aquisition flow
In a cardiac SPECT study, typically 64 projections are obtained over 180 degrees at 3- degree increments, and each projection usually takes about 20 seconds.
LET
amount of energy deposited per length of absorber
(keV/um)
electomagnetic and beta- have low LET
alpha- have high LET
Using AC and resolution compensation
Reduces number of false positives
Rubidium-82 source
Rubidium-82 is the daughter of strontium-82 (half-life = 25 days) and is eluted from a strontium-82/ rubidium-82 generator. The other PET agents are produced in medical cyclotrons.
Caution: High Radiation Area sign
NRC regulation states that when an individual could receive a dose > 500 rads per hour at 1 m from the source, area should have the “Caution: High Radiation Area sign posted”.
Transportation index
Exposure measurement at 1 m from the surface of the package.
Well counter
A well counter is a device used for measuring radioactivity in small samples. It usually employs a sodium iodide crystal detector. It was invented in 1951 by Hal Anger, who is also well known for inventing the scintillation camera.
MAX dose to fetus
500 mrem
Effect of LVH on SPECT images
LVH may improve count statistics, which results in better-quality images with the risk of hiding small areas of ischemia.
Effect of prone imaging
Prone imaging (patient lies on abdomen) provides greater separation between the heart and the diaphragm, so there is less inferior wall attenuation in comparison to a supine image (patient lays on back).
ANEDONSINE receptors
A1 - AV node
A2A - target
A2B/A3 - bronchial
DIPYRIDAMOLE
Dipyridamole is primarily metabolized in the liver and should be used cautiously in patients with hepatic dysfunction. The biologic half-life of dipyridamole is 30 to 45 minutes. Adenosine but not dipyridamole is rapidly taken up by red blood cells and endothelial cells, and this explains the short biologic half-life of adenosine. The longer half-life makes it a good agent for PET imaging as it does not need to be given.
Why also exercise when giving vasodilators?
The patients usually undergo a low-level exercise without achieving target heart rate in order to minimize side effects of vasodilators and facilitate the clearance of tracer activity from the liver and gut
Duke score
DTS = exercise time (in minutes) – [5 × (amount of ST-segment deviation in mm) – 4 × exercise angina index
MPI sensitivity to detect obstructive CAD
85%
LV dilation on SPECT without ischemia
hypertensive heart disease
Intrinsic or extrinsic uniformity
daily
Resolution and linearity
once a week
center of rotation
once a month
Collimator integrity
once a year
test linearity of camera
four-bar phantom is placed between the cobalt-57 sheet and the collimator
test intrinsic uniformity of system
remove collimator,
test with single 99mTc point source
test extrinsic uniformity of system
planar sheet of 10-15 mCi of Co-57 is placed ON TOP OF COLLIMATOR
Tc reduction
Technetium is eluted in the form of sodium pertechnetate via ion exchange with chlorine in the alumina column. In sodium pertechnetate, the oxidation state of technetium is +7, its most stable oxidation state. It is reduced to +5 and +4 before labeling.
Increased levels of pertechnetate (99mTcO4-)
99mTc-labelled macroaggregated albumin
99mTc-labelled macroaggregated albumin localizes predominately in the lungs and is used for lung perfusion.
hydrolyzed reduced 99mTc
hydrolyzed reduced 99mTc as TcO2 or 99mTc-stannous colloid localize mainly in the liver
1/2 life 15O
122 sec
1/2 life 82Rb
75 sec
1/2 life 18F
110 min
1/2 life 123I
132 hous
123I-MIBG
123I is used in the MIBG scan for patients with heart failure and has prognostic value. The cardiac sympathetic nervous system can be imaged noninvasively using 123I-MIBG tracer. The reduced heart-to-mediastinum (H/M) ratio uptake of123I-MIBG has been associated with worse cardiovascular outcomes, including ventricular arrhythmia and death.
MISADMINISTRATION
Administering the wrong radiopharmaceutical to a person, by a route other than the route prescribed by the authorized physician, to a part of the body other than the part of the body specified by the authorized physician, a diagnostic dose of more than 50 mSv effective dose equivalent, and a therapeutic dose of more than 20% are all examples of misadministration.
MISADMINISTRATION reporting
The NRC, not the FDA, should be informed about the misadministration of a radioactive tracer. The NRC must be notified by the next calendar day by telephone after the misadministration, and a written report must be submitted no later than 15 days after the event.
Cardiotoxicity by MUGA
LVEF decreased by 10% and is lower than 50%
Only technique that quantifies RV
Gated blood pool SPECT
but NOT
First-pass ventriculography
Minimum counts per pixel
A minimum of 200 counts/ pixel using technetium-99m and 100 counts/ pixel using thallium-201 in the myocardium on an anterior projection is recommended.
Off peak uniformity test
What type of breathing is best when using CT for attenuation correction?
tidal breathing
half value thickness (layer) for 99mTc photons in tissue
about the same as water
Sinogram
A sinogram is a single row of pixels, repeated for each planar projection. Each sinogram is used to reconstruct a single transaxial slice.
Alumina breakthrough from a 99mTc generator is evaluated by
Colorimetric test
What is the main photon energy of 99Mo
740 and 780 Kev
Caution, radioactive material
Caution, radioactive material
Caution, radiation area
Caution, high radiation area
Dose to organ limit (annual REM)
Lens of the eye limit (annual REM)
Extremity annual limit (REM)
Skin annual limit (REM)
member of public (annual REM)
misadministration
AND >50 mSev total body
OR
> 0.5 Sev organ
Limits fr DOT labelling
11C-hydroxyephedrine
11C-hydroxyephedrine is used to depict sympathetic innervation of the myocardium.
11C-acetate
11C-acetate is a marker of myocardial oxidative substrate metabolism.
Because 11C-acetate has a high first-pass myocardial extraction fraction, images obtained early following tracer injection can also be used to measure regional tissue blood flow,
